Can You Inject Botox and Filler at the Same Time in the Same Place?

Thank you for the question.
You can combine injectables to personalize your treatment.  I perform this as part of a "Liquid Lift".  Neuromodulators like Botox can relax frown lines and hyaluronic acid injectables can lift the crease left behind.  Studies have shown that the results of hyaluronic acid injectables last longer when used in tandem with Botox.
As always, an in-person consultation with a board certified dermatologist with cosmetic training is the best way to assess your needs and provide medical advice. 

If the vertical lines between the eyebrows are very deep, they may need filler to help flatten them, but if you are not in a rush, and can wait for several sessions of Botox to keep the muscles relaxed (usually reinject every four months), the lines may fade away. If you wish to have the lines go away faster, I would normally recommend evaluating the result of the Botox two weeks after the injection before a filler is placed, unless you have a social function in the near future and wish to look your best for it. In that event, I would inject the filler first, and immediately after place the Botox to avoid displacement of the Botox that could occur if the order were reversed.

Yes, the two can be done at the same time, butI often have my patients stage it. The Botox is a paralytic, and will prevent you from making the wrinkle.  Once it is in effect ( a week), I then use the filler to mask the lines.  Sometimes, if you do them at the same time, you push the filler out of the way everytime you make that wrinkle because the muscle is still active ( it takes 3-5 days for the Botox to kick in).  I hope this helps.